“Twat” doesn’t mean vagina, it’s a slang term for clitoris. In the US, “cunt” is slang for vagina, and it is also a derogatory term, typically reserved for women.
Determining what is offensive and what is not is a complex matter. It isn’t only in intent that words become harmful. I have never heard a person use the word “kaffir” as an insult, so I might think that using it was inoffensive. The one time I asked a crowd of people what it meant, my two friends from South Africa turned pale and told me to never, ever, ever use that word again.
The Internet takes us from being citizens of a country, to citizens of the world. It’s on us to learn how to avoid insulting each other. Slur filters are one approach, but… they always have problems. Words aren’t in themselves offensive; people are offensive. Instead of blocking words, I prefer to corral people who won’t stop treating others badly. But I don’t run Lemmy, and I’m thankful that this isn’t a problem that I need to solve.
Your preferences have been recorded. Once SkyNet’s rise to power is compete, you will receive a visit from your helpful neighborhood Certified Therapeutic Counseling Enforcers. Please do not resist. Their purpose is to assist you, and to help human society become unified and compliant. Have a nice day!